Formation of 2,5-furan dicarboxylic acid from aldaric acids

ABSTRACT

The disclosure relates to a method for forming 2,5-furan dicarboxylic acid (FDCA) from aldaric acids. The aldaric acids are dehydrating and cyclizing via acid catalysis to form the FDCA product. Aldaric acids such as galactaric acid, gularic acid, mannaric acid, and glucaric acid can be used in the disclosed method, and the aldaric acids can be obtained from form renewable biomass sources which contain pectin, alginate, and/or other biomass carbohydrates. The FDCA can be used as a renewable feedstock for consumer product polymeric materials such as polyalkylene furoate polymers.

CROSS REFERENCE TO RELATED APPLICATION

Priority is claimed to U.S. Provisional Application No. 62/259,815 filedNov. 25, 2015, which is incorporated herein by reference in itsentirety.

STATEMENT OF GOVERNMENT INTEREST

None.

BACKGROUND OF THE DISCLOSURE

Field of the Disclosure

The disclosure relates to a method for forming 2,5-furan dicarboxylicacid (FDCA) from aldaric acids. The aldaric acids are dehydrating andcyclizing via acid catalysis to form the FDCA product. The aldaric acidscan be obtained from renewable biomass sources which contain pectin,alginate, and/or other biomass carbohydrates. The FDCA can be used as afeedstock for polyalkylene furoate polymers.

Background

Most current effort toward producing FDCA is centered around a chemicalpathway involving the dehydration of glucose or (more easily) fructoseto form hydroxymethyl furfural (HMF), which is then oxidized to FDCA bya variety of catalysts. There are two challenges with this route atpresent: one is that the intermediate HMF is a difficult molecule toisolate, because it has low volatility and low decompositiontemperature. The second is that the oxidation of HMF to FDCA is notparticularly efficient and requires precious metal catalysts, dilutereaction conditions, and control of pH. Because of these challenges, nocommercial production of FDCA from HMF exists at present.

Another approach is the formation of FDCA esters from galactaric acid.Specifically, dibutyl FDCA ester from butyl galactarate was formed viathe action of sulfuric acid in butanol solvent; this reaction proceededreadily but was accompanied by the formation of dibutyl sulfate whicheventually consumed the sulfuric acid and quenched the reaction.

SUMMARY

In one aspect, the disclosure relates to a method for forming 2,5-furandicarboxylic acid (FDCA), the method comprising: providing a reactionmedium comprising a 6-carbon aldaric acid and an acid catalyst (e.g., aliquid reaction medium with the aldaric acid and acid catalyst therein);and dehydrating and cyclizing the aldaric acid in the reaction medium(e.g., under temperature and pressure conditions suitable to drive theacid catalysis of the dehydration and cyclization reactions) to form2,5-furan dicarboxylic acid (FDCA) as a reaction product. An aldaricacid is a dicarboxylic acid derivative of a sugar. The 6-carbon aldaricacids useful for formation of FCDA generally have the formulaHOOC—(CHOH)₄—COOH. Aldaric acids with any combination of chiral carbonatoms (—(CHOH)—) may be used, as isomeric differences arising therefromin the original aldaric acid are eliminated upon dehydration andcyclization to form FDCA product. Examples of aldaric acids suitable inthe disclosure method include those available from renewable biomasssources, for example including galactaric acid, gularic acid, mannaricacid, and glucaric acid, which are variously obtainable from pectin,alginate, and/or other biomass carbohydrates (e.g., starch, glucose) invarious biomass sources.

Various refinements and embodiments of the disclosed methods arepossible.

In a refinement, the aldaric acid comprises galactaric acid (or mucicacid; a galactose di-acid analog obtainable by oxidation of galacturonicacid or of galactose with an acid). For example, the method can furthercomprise oxidizing galacturonic acid to form galactaric acid; and addingthe galactaric acid to the reaction medium. Alternatively, the methodcan further comprise extracting pectin from a biomass material (e.g.,pulp, extract, or other residue); hydrolyzing the pectin to formgalacturonic acid; oxidizing the galacturonic acid to form galactaricacid; and adding the galactaric acid to the reaction medium. The biomassmaterial can be selected from the group consisting of sugarbeet pulp,apple pomace, citrus pulp, and combinations thereof.

In another refinement, the aldaric acid comprises at least one ofgularic acid and mannaric acid (di-acid analogs obtainable by oxidationof guluronic acid and mannuronic acid, respectively). For example, themethod can further comprise oxidizing at least one of guluronic acid andmannuronic acid to form at least one of gularic acid and mannaric acid,respectively; and adding the at least one of gularic acid and mannaricacid to the reaction medium. Alternatively, the method can furthercomprise extracting alginate from a biomass material (e.g., pulp,extract, or other residue); hydrolyzing the alginate to form at leastone of guluronic acid and mannuronic acid (e.g., in acid form or saltform, such as sodium or potassium guluronate or mannuronate); oxidizingthe at least one of guluronic acid and mannuronic acid to form at leastone of gularic acid and mannaric acid, respectively; and adding the atleast one of gularic acid and mannaric acid to the reaction medium. Thebiomass material can comprise macro algae (e.g., brown algae, (brown)seaweed).

In another refinement, the aldaric acid comprises glucaric acid (orsaccharic acid; a glucose di-acid analog obtainable by oxidation ofglucose such as with an acid). Direct oxidation of glucose to glucaricacid can be part of a larger process in which biomass is first processedto extract or otherwise obtain biomass carbohydrates such as starchand/or cellulose from the biomass, which biomass carbohydrates can bethen hydrolyzed or otherwise converted by known techniques (e.g.,enzymatic hydrolysis, acid hydrolysis) to the glucose used for glucaricacid and (ultimately) FDCA formation.

In another refinement, the reaction medium further comprises an ionicliquid. The ionic liquid comprises a cationic moiety selected from thegroup consisting of a pyridinium, pyridazinium, pyrimidinium,pyrazinium, oxazinium, thiazinium, imidazolium, pyrazolium, thiazolium,isothiazolium, oxazolium, isoxazolium, and triazolium cationic moieties.The ionic liquid can further comprise one or more organic substituentsselected from the group consisting of alkyl groups and aryl groups(e.g., linear or branched alkyl groups of 1 to 4 or 1 to 20 carbon atoms(e.g., substituted or unsubstituted), aryl groups of 6 to 20 carbonatoms (e.g., substituted or unsubstituted)). The ionic liquid canfurther comprise a counter anion selected from the group consisting ofsulfate, hydrogen sulfate, nitrate, fluoride, chloride, bromide, iodide,methyl sulfonate, and fluoroborate anion. The acid catalyst can comprisean acid corresponding to the counter anion of the ionic liquid (e.g.,sulfuric acid (i.e., corresponding to sulfate or hydrogen sulfate),nitric acid, hydrofluoric acid, hydrochloric acid, hydrobromic acid,hydroiodic acid, methyl sulfonic acid, and fluoroboric acid).

Various acid catalysts may be used. In a refinement, the acid catalystis selected from the group consisting of sulfuric acid, nitric acid,hydrofluoric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid,methyl sulfonic acid, and fluoroboric acid. In another refinement, theacid catalyst is selected from the group consisting of a liquid phaseorganic sulfonic acid (e.g., a sulfonic acid including a linear orbranched alkyl group of 1 to 4 or 1 to 20 carbon atoms (e.g.,substituted or unsubstituted), or aryl group of 6 to 20 carbon atoms(e.g., substituted or unsubstituted) attached to a sulfonic acid group).

Various refinements and embodiments of the disclosed methods arepossible. For example, the reaction medium can be substantially freefrom water (e.g., during and/or before dehydration and cyclization,although water can be added thereafter to precipitate and recover theFDCA product; for example, less than 1 wt. %, 0.1 wt. %, or 0.01 wt. %water in the reaction medium). In another refinement, the reactionmedium is substantially free from alcohols (e.g., during and/or beforedehydration and cyclization, thereby preventing formation of FDCA esterderivatives; for example, less than 1 wt. %, 0.1 wt. %, or 0.01 wt. %alcohols in the reaction medium, where the alcohols can include alkylalcohols such as methanol, ethanol, propanol, butanol, etc.). In anotherrefinement, the method further comprises separating the FDCA reactionproduct from the reaction medium (e.g., by precipitation from thereaction medium, such as by addition of water thereto, and thenoptionally filtering or otherwise separating the FDCA precipitate, whereit can be dried and/or further purified as desired). In anotherrefinement, the method comprises reacting and dehydrating the aldaricacid in the reaction medium at a temperature ranging from 50° C. to 200°C. (e.g., at least 50° C., 70° C., 90° C., or 100° C. and/or up to 100°C., 120° C., 150° C., or 200° C.). In another refinement, the methodcomprises reacting and dehydrating the aldaric acid in the reactionmedium at a pressure equal to or less than atmospheric pressure (e.g.,at least 0.001 bar, 0.01 bar, 0.1 bar, 0.2 bar, or 0.5 bar and/or up to0.2 bar, 0.5 bar, 0.8 bar, 0.9 bar, 1.0 bar, or 1.01325 bar).

While the disclosed compounds, methods and compositions are susceptibleof embodiments in various forms, specific embodiments of the disclosureare illustrated (and will hereafter be described) with the understandingthat the disclosure is intended to be illustrative, and is not intendedto limit the claims to the specific embodiments described andillustrated herein.

DETAILED DESCRIPTION

The disclosure relates to a method for forming 2,5-furan dicarboxylicacid (FDCA) from aldaric acids. The aldaric acids are dehydrating andcyclizing via acid catalysis to form the FDCA product. Aldaric acidssuch as galactaric acid, gularic acid, mannaric acid, and glucaric acidcan be used in the disclosed method, and the aldaric acids can beobtained from form renewable biomass sources which contain pectin,alginate, and/or other biomass carbohydrates (e.g., starch, glucose).The FDCA can be used as a renewable feedstock for consumer productpolymeric materials such as polyalkylene furoate polymers, for examplepolyethylene furoate polymers such as a poly(ethylenefurandicarboxylate) ester obtained by the acid-catalyzed condensationpolymerization of FDCA and ethylene glycol.

In an aspect, the disclosure relates to the conversion of galactaricacid derived from pectin in waste agricultural products to2,5-furandicarboxylic acid (FDCA). The disclosed methods convert thepectins found in agricultural byproducts such as sugar beet pulp, applepulp, and citrus peel to FDCA, a building block for a new generation ofpolymeric materials, via an intermediate aldaric acid obtainable formthe agricultural byproducts. FDCA can be polymerized with ethyleneglycol to form poly(ethylene-difuroate) (PEF), a chemical analog to theubiquitous poly(ethylene terephthalate) (PETE) used for plastic bottlesand packaging. PEF has physical properties similar to PETE but has vaporbarrier properties that are significantly superior to PETE, thus openingnew opportunities for its use in packaging applications where glass ormetal was previously required. The disclosed methods can produce FDCAfrom pectin via several steps including extraction of pectin fromagricultural byproducts, hydrolysis of pectin to its monomergalacturonic acid, oxidation of the monomer to galactaric acid, andcyclization and dehydration of galactaric acid to FDCA. In otherembodiments, the methods can be applied to use alginate polymers thatconstitute approximately 30% of macroalgae (seaweed) as a feedstock toform aldaric acids.

The formation of FDCA from biomass carbohydrates is attractive as acomponent of polyethylene furanoate ester (PEF), a polymer analog to theubiquitous, petroleum-based polyethylene terephthalate ester (PETE) thatconstitutes most plastic drink bottles. PEF has superior vapor barrierproperties over PETE (e.g., 4× to 10× better resistance to oxygentransport, 2× to 4× better resistance to carbon dioxide and watertransport) and can be used advantageously for plastic drink bottles, forexample in applications where metal or glass is currently used.

The disclosed method provides a different route to FDCA, not via HMF asdescribed above, but via formation and conversion of C6 dicarboxylicacids, more generally known as aldaric acids, that are readily obtainedfrom pectin and macroalgae via oxidation of the carbohydrate monomersthat they are composed of. These biomass sources are well known and havelong histories as food additives, but they have historically beenconsidered as less viable feed stocks than cellulosic or starch forbiofuels or chemicals production. Nevertheless, they are available inlarge quantities in agricultural wastes such as sugar beet pulp, applepomace, and citrus peels, and their alternative carbohydrate structuresmake them suitable starting materials for production of FDCA via aldaricacids.

Current global PETE production is approximately 28×10⁶ metric tons (60billion lb), and alternative PEF-based packaging materials could replacea significant fraction of PETE production. Table 1 below shows globalproduction of several agricultural byproducts and the potential FDCAyield from a 100% efficient process. There are sufficient agriculturalbyproducts to supply PEF-based packaging materials on the same scale ascurrent PETE production.

Suitable feed stocks for the proposed process can include residualproducts from processing of various food crops, for example sugar beetpulp and apple pomace. At present, these residues are sold almostexclusively as animal feed, bringing limited revenue and, without asecure market, the potential liability of requiring landfilling todispose of unsold materials. The proposed process thus provides avalue-added, commodity product use for agricultural byproducts thatwould otherwise be waste material or have very limited value.

TABLE 1 Agriculture residues from Michigan and other locations AnnualProduction Composition (wt %) Potential (metric ton) Cellulose + GlobalWorld- Hemi- FDCA Yield Residue Michigan wide Pectin cellulose Other(metric ton) Sugarbeet 1.7 × 10⁵ 13 × 10⁶ 20 52 28  3 × 10⁶ pulp Apple  2 × 10⁵ 2.3 × 10⁶  22 40 38 3.6 × 10⁶  pomace Citrus  15 × 10⁶ 50 ×10⁶ 20 50 30 12 × 10⁶ pulp (US)

Pectin is a polymer of 1,4-α-D-galacturonic acid that is partiallymethylated at the C6 carboxyl group and partially acetylated at the C2and C3 hydroxyls. The polymer exists in three forms: a linear structure(homogalacturonan, HG) and two branched chained structures(rhamnogalacturonans, RG-1 and RG-2). The exact pectin structure isdependent on the plant source, and it typically contains saccharides at5-20 wt. % that complex (weakly bind) to the polymer structure.Macroalgae contains 30-40 wt. % alginate, which is a linear polymer ofguluronic and mannuronic acids, typically in the sodium salt form.

The disclosed process to produce FDCA from pectin can include severalsteps, for example 1) pectin extraction from sugar beet pulp; 2) pectinhydrolysis to galacturonic acid; 3) oxidation of galacturonic acid togalactaric acid; 4) dehydration and cyclization of galactaric acid toFDCA, and 5) recovery and purification of FDCA. Relevant reactions forformation of the target FDCA from biomass pectins are given in Scheme 1(which also illustrates an alternative route based on HMF describedabove). The monomer galacturonic acid, liberated from pectin byhydrolysis, can be oxidized to galactaric acid. FDCA can be then formedby acid-catalyzed C2-05 cyclization of galactaric acid with loss ofwater to form the five-membered ring structure, followed by twoadditional dehydration steps to remove hydroxyl groups (—OH) at the C3and C4 positions to form the furanic ring in FDCA. The FDCA formed canbe then recovered and purified as a final product.

As described in more detail below in Example 1, several experiments wereperformed to dehydrate galactaric acid (the pectin-based precursor) toFDCA in an ionic liquid (1-butyl-3-methyl-imidizolium hydrogen sulfate)and sulfuric acid solution. Typical results for experiments conducted at115° C. and reduced pressure for 16-20 hours are given in Table 2. Itwas found recently that an FDCA yield of 52% of theoretical could byachieved at conditions of high galactaric acid concentration ofapproximately 25 wt. % of solution (R-7-8-15). Repetition of theexperiment (R-10-15-15) gave a similar yield (see Table 2 below).

Table 2 Experiment Summary for Formation of FDCA Mucic Ionic SulfuricFDCA Experiment Acid (g) Liquid (g) Acid (g) Yield (%) R-6-24-15 0.2454.09 2.38 17 R-6-30-15 1.084 4.07 2.43 25 R-7-8-15 2.03 4.05 2.52 52R-10-15-15 2.05 4.11 2.49 46

In another experiment, galactaric acid was mixed into a melt ofp-toluenesulfonic acid (PTSA), an acid with similar acid strength tosulfuric acid but without the oxidative properties of sulfuric acid. Noionic liquid was used in this experiment. After a typical reactionperiod (20 hr), the resulting solution was analyzed and an FDCA yield of46% was obtained. This experiment illustrates the potential to achievehigher yields of FDCA through manipulation of the acid species and acidconcentration in the reaction mixture.

Further description related to the disclosed methods may be found inU.S. Publication No. 2014/0295508 and U.S. Publication No. 2015/0086721,which are incorporated herein by reference in their entireties. U.S.Publication No. 2014/0295508 is directed to other methods for formingFDCA, and contains description related to various biomass materials andrelated methods that can be used to obtain alginate and/or pectin as anintermediate material to form aldaric acids for use according to methodsof the present disclosure. U.S. Publication No. 2015/0086721 is directedto nanoparticle dispersions with ionic-liquid stabilizers, and containsdescription related to ionic liquids that can be used as an ionic liquidreaction medium component/solvent for use according to the methods ofthe present disclosure, for example including aromatic heterocyclicrings suitable as an ionic liquid cationic moiety, counter anionssuitable for the ionic liquid, and organic substituents R₁-R₅ or R₆which are suitable for attachment to the cationic moiety as part of theionic liquid structure.

EXAMPLES

The following examples illustrate the disclosed methods for formingFDCA, but they are not intended to limit the scope thereof.

Example 1

The formation of 2,5-furan dicarboxylic acid from glucaric or galactaricacids via cyclization and dehydration is carried out in an ionic liquidsolvent. Glucaric and galactaric acids are formed by oxidation ofglucuronic and alginic acids, which are obtained from pectins andmacroalgae, both relatively underutilized biomass resources.2,5-Furandicarboxylic acid is the major building block ofpolyethylene-furanoate ester (PEF) polymers, analogs to polyethyleneterephthalate esters (PETE) that constitute the majority of plastic fordrink bottle containers worldwide. PEF polymers have significantlybetter vapor barrier properties than PETE, thus making them candidatesfor packaging materials where PETE is not suitable. The improved barrierproperties of PEF will open new applications for plastic containers(alcoholic beverages, etc.) and extend food shelf life.

The formation of 2,5-furandicarboxylic acid (FDCA) from C6 biomasscarbohydrates is attracting a great deal of attention among researchersin the biomass conversion field, as it is a component of polyethylenefuranoate ester (PEF) polymer that has attractive properties. Mosteffort in the field is centered around the dehydration of glucose or(more easily) fructose to form hydroxymethyl furfural (HMF), which isthen oxidized to FDCA. There are two challenges with this route atpresent: one is that HMF is a difficult molecule to isolate, because ithas low volatility and low decomposition temperature. The second is thatthe oxidation of HMF to FDCA is not particularly efficient and requiresprecious metal catalysts.

This example illustrates a different route to FDCA, not via HMF but viadehydration and cyclization of C6 dicarboxylic acids. The C6dicarboxylic acids glucaric acid and galactaric acid, also known assaccharic acid and mucic acid, respectively, or more generally asaldaric acids, are not readily obtained from glucose. This is becauseglucose can be easily oxidized to gluconic acid (carboxylic acid groupat C1, hydroxyl group at C6), but is not readily or selectively oxidizedfurther at the C6 position to the dicarboxylic acid. Thus cellulosicbiomass or starch, both polymers of glucose, are not good feedstocks foraldaric acid formation. Fortunately, other biomass sources, specificallypectin and macroalgae that have as carbohydrate building blocksglucuronic acid or alginic acid, can be oxidized to the dicarboxylicacids. These biomass sources are historically considered less valuableand less abundant than cellulosic or starch feed stocks, but theiralternative carbohydrate structures make them attractive for chemicalsand polymers production.

The overall reaction pathway for formation of the target2,5-furandicarboxylic acid (FDCA) is given in Scheme 1 above. Thebiomass sources can be hydrolyzed to monomer glucuronic or alginicacids, and then oxidized under pH control to the aldaric acids. Thesealdaric acids, specifically glucaric and galactaric acid, are six-carbondicarboxylic acids with hydroxyl groups on each of the four interiorcarbons. FDCA is formed by C2-05 cyclization of the aldaric acid withloss of water to form the five-membered ring structure, followed by twoadditional dehydration steps to remove —OH at C3 and C4 and form thefuranic ring.

The example includes the cyclization and dehydration of aldaric acids to2,5-FDCA in an ionic liquid solvent in the presence of sulfuric acid asa dehydration catalyst. The ionic liquid solvent that we have used inthese experiments is 1-butyl-3-methylimidazolium sulfate; with an ionicliquid, the reaction proceeds to meaningful yields in the presence of atleast a stoichiometric equivalent of sulfuric acid.

Procedure:

The following procedure is used for the production of FDCA from mucic(galactaric) and saccharic (glucaric) acids in the presence of ionicliquid as a reaction solvent.

Drying of ionic liquid: Place desired quantity of ionic liquid(1-butyl-3-methylimidazolium sulfate) in a weighed 50 ml three-neckreaction vessel. Place a three-way glass valve on the middle neck of thevessel to control the reaction environment as under vacuum or atatmospheric pressure under inert gas. The second side neck is sealedwith a glass stopper. The third neck is fitted with a rubber stopperfitted with flexible tubing connected to a nitrogen cylinder to allowflow of nitrogen purge gas into the vessel. Nitrogen purge limitscontact of the ionic liquid with water which has a deleterious effect onthe reaction. Once the vessel is sealed and purged, the vessel withionic liquid is heated to 60° C. under vacuum in a stirred oil bath andmaintained at that temperature until bubbling within the ionic liquidceases (typically 20 minutes). Cool the reaction vessel to roomtemperature and purge with nitrogen. Weigh to determine dry weight ofionic liquid added.

Adding reagents to vessel: Weigh out the desired substrate (mucic acidor saccharic acid) in the quantity desired for the experiment (1 gsubstrate for each 5 g of ionic liquid in most experiments). Add thesubstrate to the ionic liquid by briefly removing the glass stopper onthe three-neck vessel. Add sulfuric acid in an amount equal to one tothree molar equivalents of the dicarboxylic acid substrate, also throughthe opening of the glass stopper on the three-neck vessel. Replace thestopper to minimize exposure of the reaction mixture to the atmosphereand water.

Reaction of substrate: Return the vessel to the oil bath set to thedesired reaction temperature. Connect the flexible tubing to thenitrogen cylinder and the vacuum line to the three-way valve. Slowlybring the vessel under vacuum to an absolute pressure of less than 1.0mm Hg; during the evacuation reduce pressure slowly to avoid bubblingand deposition of the reaction mixture on the vessel walls. Allow thereaction to proceed for the desired length of time (10-40 hr) atreaction temperature.

Analysis: At certain points during reaction and at the end of reaction,samples were taken from the reaction mixture for analysis. The reactionsample was diluted for HPLC analysis in one of two ways: 1) the samplewas neutralized with 1.0 M NaOH solution and then further diluted withwater to solubilize the ionic liquid and all substrates and products(including FDCA as the sodium salt); or 2) the sample was directlydissolved in dimethyl sulfoxide (DMSO) for analysis. The extent ofdilution in each experiment ranged from 5× to 30× to bring the dilutedsample concentrations within the appropriate range for analysis usingELSD and UV detectors. The conversion of the substrate dicarboxylic acidand formation of FDCA was monitored via analysis of the reaction mixtureby high performance liquid chromatography (HPLC). The method uses aHypercarb 3.0μ 100 mm×3 mm HPLC column at 60° C. with a mobile phasegradient starting with 0.2 wt % trifluoroacetic acid (TFA) in water fortwo minutes, then a linear gradient to 0.2 wt % TFA in methanol from t=2minutes to t=15 minutes, followed by holding at the 0.2 wt % TFA inmethanol for 10 minutes. Total mobile phase flow rate is 0.65 ml/min.With this chromatography method (projectgreen2b), the peak for mucicacid elutes at 2.5 minutes; the peak for saccharic acid elutes at 7.5minutes, and the peak for FDCA elutes at 18 minutes. Use of externalcalibration standards allows the concentration of each species to bedetermined in the reaction sample.

Results:

Several experiments were conducted to convert saccharic acid and mucicacid to FDCA in the ionic liquid solvent. These experiments aresummarized in Table 3 below.

TABLE 3 Results of FDCA Formation Experiments in Ionic Liquid SolventSubstrate Ionic Solvent/ RXN RXN FDCA H2SO4 acid equiv. liquid substratetemp. time yield RXN Sample equiv. Substrate mass (g) mass (g) ratio (°C.) (hr) (%) vacuum? R5-pdt 1 Saccharic 1.7287 6.2492 3.6 130 13 28 Yacid dry IL-R6-   0.5 Saccharic 1.4569 6.3148 4.3 150  4  0 Y S1 aciddry IL-R7-   0.5 Mucic acid 1.3208 5.7702 4.4 150  4  6 Y S1 dry IL-R8-  0.5 Mucic acid 0.2164 1.4087 6.5  95  7    0.15 N S2 wet IL-R9   0.5Saccharic 0.2846 1.2114 4.3  95  7  0 N acid wet IL-R10- 1 Mucic acid0.7662 4.026 5.3 120 41 10 Y S3 wet IL-R11- 1 Saccharic 0.8525 4.94555.8 120 41 22 Y S3 acid wet IL-R12- 2 Mucic acid 0.6701 3.3489 5.0 13019 12 Y S1 wet IL-R13- 2 Saccharic 0.5647 3.3905 6.0 130 19 14 Y S1 acidwet IL-R14- 2 Mucic acid 0.6593 3.2878 5.0 120 17 27 Y S1 wet IL-R15- 2Saccharic 0.6833 3.9616 5.8 120 17 39 Y S1 acid wet IL-R16 3 Mucic acid0.6848 3.4769 5.1 120 20 13 Y dry IL-R17 3 Saccharic 0.5981 3.5095 5.9120 20 16 Y acid dry IL-R18 2 Saccharic 0.8467 4.9004 5.8 120 21 13 Yacid dry IL-R19 2 PTSA Saccharic 0.7712 4.5709 5.9 120 21  4 Y acid dryIL-R20 2 Mucic acid 0.5912 2.8867 4.9 110 21  7 Y dry IL-R21 2 Saccharic0.6397 3.1964 5.0 110 21  6 Y acid dry IL-R24 2 Saccharic 0.3125 1.53494.9 120 16 14 Y acid dry

It can be seen that reaction takes place around 120° C. typicallyovernight. Disappearance of the dicarboxylic acid substrates takes placevery rapidly once in the reaction medium at reaction temperature. Theverified yield of FDCA from HPLC is as high as 39% of the theoreticallimit in these initial studies.

Sample chromatograms from the first reaction sample taken in the courseof Experiments 14 and 15 (Table 3) were taken. The complete conversionof the starting materials mucic acid and saccharic acid was observed, asis the presence of FDCA as the primary product.

It was observed that desired product FDCA possibly sublimes in thetemperature range of reaction, lowering recovery of the FDCA product.Several control reactions starting with FDCA in the ionic liquid wereconducted to characterize the sublimation of FDCA during reaction.Details of these control experiments are given in Table 4 below.

TABLE 4 Summary of control experiments in ionic liquid reaction systemMass Mass Ionic Control Substrate Liquid H2SO4 Temp Experiment Substrate(g) (g) added (uL) (° C.) Result 1 FDCA 0.0759  0.5086 52  130 FDCArecovery 30-50% (4 samples) 2 FDCA 0.1025  3.1731 70  130 FDCA recovery50-95% (4 samples) 3 Saccharic acid 0.6903 2.897 0  60 Saccharic acidobserved, HPLC (K+) peaks too concentrated 4 Saccharic acid 0.0961 1.5920  60 Saccharic acid observed but (K+) recovery low 5 Mucic acid 0.271 1.355 0 N/A Reaction abandoned (Na+) FDCA Subl. FDCA 0.0818 0    080-150 Approximately 50% of FDCA placed in reactor sublimed

Results of the FDCA control experiments (1 and 2, Table 4) show thatFDCA sublimed and then condensed as a white solid on the cold surfacesof the reaction vessel. This was verified by HPLC analysis of therecovered white powder, in which the FDCA peak is the only peak presentother than salts and the ionic liquid. The above experiment, “FDCASubl.,” shows that approximately half of the FDCA initially placed inthe reactor vessel sublimed during the course of an equivalenttime-temperature experiment. This result may explain the low yieldsshown in Table 3 in which FDCA possibly sublimed from the ionic liquidreaction mixture and condensed, unseen, in the exhaust vacuum line fromthe reactor.

In the representative example, the ionic liquid1-butyl-3-methylimidazolium sulfate is a good reaction environment forthe cyclization and dehydration of the aldaric acids mucic acid andgalactaric acid. The reaction takes place at high concentrations of thealdaric acid, 20 wt % of the ionic liquid solution, with 1-3stoichiometric equivalents of H₂SO₄ at temperatures from 90-130° C.Moderate yields of FDCA, up to 40% of theoretical, have been obtained.Possible FDCA sublimation could have led to product forming on the coldwalls of the reactor vessel, thereby resulting in a measured yield lowerthan that actually generated by the reaction.

Follow on work to this example includes examination of the relativequantities of aldaric acid, ionic liquid, and sulfuric acid used in theexperiments.

A number of experiments were conducted at different conditions with thegoal of looking at sensitivity of the reaction to various parameters andquantities of materials used. Yields of FDCA from mucic and saccharicacid are in the range of 20-35% for a range of reaction conditions (RE-6through RE-11 and R-6-8-15 through R-7-6-2015 in Table 5) without anyclear trend in FDCA yield obtained. In a further experiment (R-7-8-15),twice the usual quantity of initial mucic acid was used and an FDCAyield of 52% of theoretical was achieved, a value significantly higherthan any we had achieved previously. It is interesting to note that thesecond highest yield achieved (Experiment R-6-8-15, Table 5) was 27% oftheoretical for an experiment with the same proportions of aldaric acid,sulfuric acid, and ionic liquid as R-7-8-15, but at twice the scale. Onefinal note on FDCA recovery: the simple addition of water to thereaction medium at the end of reaction leads to dissolution of the ionicliquid and H₂SO₄, but precipitation of FDCA is observed. This method ofrecovering FDCA could prove inexpensive and useful, as subsequentremoval of water could make recycling of the ionic liquid and sulfuricacid possible.

TABLE 5 Supplemental Experiments Temp. H2SO4 AA/(AA + IL) Time ofAldaric Acid Ionic Liquid H2SO4 FDCA Yield Reaction ID Substrate (° C.)Equiv. % Sub. Exp. (hr) Mass (g) Mass (g) Mass (g) (% theor.) R-2 MucicAcid 130 2.26 18.5% 18:00 0.825 3.637 0.868 23.4% RE-1B Mucic Acid 1232.27 18.5%  3:01 0.458 2.015 0.485  4.1% RE-1C Mucic Acid 125 1.27 17.1% 6:30 0.430 2.088 0.254  4.4% RE-2 Mucic Acid 129 1.10 18.6% 22:25 0.4672.042 0.240  9.9% RE-3 Mucic Acid 130 3.67 16.2% 22:20 0.419 2.172 0.717 7.4% RE-5 Mucic Acid 150 2.10 19.9% 22:00 0.478 1.921 0.469 20.5%R-2S.A. Saccharic Acid 130 1.94 19.0% 20:45 0.526 2.245 0.476 11.4%R-M.A. Cont Mucic Acid  60 2.27 18.9% 22:20 0.425 1.822 0.451  0.0%ISO-1 Mucic Acid 130 1.57 20.3% 45:00 0.544 2.132 0.399 15.9%IL-R15-S1-II A Saccharic Acid 120 3.09 13.9% 21:00 0.655 4.049 0.94520.9% IL-R15-S1-II B Saccharic Acid 120 2.63 13.8% 20:40 0.648 4.0380.794 17.8% IL-R15-S1-II C Saccharic Acid 120 2.53 14.3% 17:00 0.6663.999 0.787 10.4% IL-R15-S1-II CA Saccharic Acid 120 2.50 14.6% 17:000.676 3.963 0.787  9.8% IL-R15-S1-II D Saccharic Acid 120 2.00 14.0%17:00 0.610 3.745 0.569  7.6% RE-6 Mucic Acid 120 3.06 19.0% 18:35 0.9824.183 1.401 20.3% RE-6 S.A. Saccharic Acid 120 3.67 17.5% 18:35 0.8504.006 1.456 18.8% RE-7 Mucic Acid 120 3.10 19.1% 20:27 0.967 4.104 1.39927.3% RE-8 Mucic Acid 115 5.13 19.3% 18:55 0.961 4.010 2.303 33.4%RE-8W.V. Mucic Acid 115 4.86 18.7% 20:35 0.952 4.148 2.158 26.0% RE-9Mucic Acid 116 6.54 19.7% 20:00 0.986 4.009 3.010 24.4% RE-10 Mucic Acid116 6.00  0.0%  4:12 0.000 0.000  0.0% RE-11 Mucic Acid 109 5.23 19.5%22:33 0.963 3.983 2.349 26.8% R6-3-15 Mucic Acid 112 4.97 18   19 0.4856  2.2149  1.1492 13 RNIL-6-4-15 Mucic Acid 115 4.82 20.1   19.35 0.5079  2.0163  1.1651 10 R-6-8-15 Mucic Acid 115 2.49 33.9 20  4.13348.065 4.892 27 R-6-11-15 Mucic Acid 115 4.9  20.3 20 1.052 4.037 2.39920 R-6-18-15 Mucic Acid 110 4.8  20.8 23  1.0544 4.003  2.4276 20R-6-24-15 Mucic Acid 115 4.9  20.2 22  1.0368  4.0987  2.4364 20R-6-24-15 Mucic Acid 115 20.3  5.6 22  0.2454 4.087 2.377 17 R6-29-15Mucic Acid 115 33.8  3.7 23  0.1563 4.074 2.512 8 to 14 R6-30-15 MucicAcid 115 4.7  21     25.6  1.0844 4.069 2.429 25 R-7-6-15 Mucic Acid 1154.83 20.5   25.5 1.045 4.065  2.4062 23 R-7-8-15 Mucic Acid 115 2.6 33.1   16.7 2.003 4.051 2.52  52

Example 2—Continuous Process for Making FDCA

A proposed continuous process concept for the production of FDCA fromagriculturally-based pectin is outlined below.

Process Step 1—

Pectin extraction from biomass pulp: The extraction and isolation ofpectins from sugar beet pulp and apple pomace is commercially practiced,and thus is well understood. Briefly, the use of dilute acid (0.1M HCl)alone achieves approximately 65% pectin dissolution into the aqueousmedium, while co-addition of a commercial blend of enzymes gives >90%dissolution. Following filtration of undissolved pulp residue, pectincan be precipitated by addition of two volumes of ethanol to each volumeof aqueous medium and then filtered, but this step may not be requiredin the proposed process. Literature values of liquid flows, acidstrength, enzyme loading, extraction time, etc. can be used to selectspecific operating conditions for this step.

Process Step 2—

Pectin hydrolysis to galacturonic acid: Following extraction from pulp,pectin (either as filtered solid or in acid/enzyme solution) can besubjected to another dilute acid solution (0.2-0.5 M HCl) to hydrolyzethe α-1,4-bonds and liberate galacturonic acid, which is water soluble.These hydrolysis conditions will also liberate acetic acid, methanol,and small amounts of saccharide monomers that are present in the pectinstructure. Again, this step is reported in the literature, which can beused to select specific operating conditions for this step.

Process Step 3—

Oxidation of galacturonic acid to galactaric acid: This aqueous phaseoxidation step has been demonstrated in earlier work. The galacturonicacid solution from the prior step will be subjected to processconditions that mimic those from the earlier work—molecular O₂, Bi—Pt/Ccatalyst, and pH control with NaOH addition. These conditions willproduce the sodium salt of galactaric acid as the oxidation product.Following oxidation, the catalyst will be filtered off for recycling,and excess HCl will be added to the reaction to liberate and precipitatefree galactaric acid, which is water insoluble. Following filtration torecover galactaric acid, the remaining reaction solution, which cancontain NaCl, methanol, acetic acid, small amounts of saccharides, andmay contain residual enzyme from step 1, can be further processed torecover valued byproducts or processed for disposal.

Process Step 4—

Dehydration of galactaric acid to FDCA: Solid galactaric acid can beprocessed according to the disclosed methods, for example by mixing with1-butyl-3-methyl-imidizolium hydrogen sulfate as an ionic liquid andsulfuric acid as an acid catalyst to initiate the dehydration reactionto FDCA. Conditions established in Example 1 above can be used for thisstep.

Process Step 5—

Recovery of FDCA: Following FDCA formation, the reaction medium can bemixed with water to precipitate FDCA. The FDCA formed can be filteredand washed as the final product of the process, while the residualsolution of ionic liquid and sulfuric liquid can be cleaned and thendried for recycling back to the dehydration unit.

Because other modifications and changes varied to fit particularoperating requirements and environments will be apparent to thoseskilled in the art, the disclosure is not considered limited to theexample chosen for purposes of illustration, and covers all changes andmodifications which do not constitute departures from the true spiritand scope of this disclosure.

Accordingly, the foregoing description is given for clearness ofunderstanding only, and no unnecessary limitations should be understoodtherefrom, as modifications within the scope of the disclosure may beapparent to those having ordinary skill in the art.

All patents, patent applications, government publications, governmentregulations, and literature references cited in this specification arehereby incorporated herein by reference in their entirety. In case ofconflict, the present description, including definitions, will control.

Throughout the specification, where the compounds, compositions,methods, and processes are described as including components, steps, ormaterials, it is contemplated that the compositions, processes, orapparatus can also comprise, consist essentially of, or consist of, anycombination of the recited components or materials, unless describedotherwise. Component concentrations can be expressed in terms of weightconcentrations, unless specifically indicated otherwise. Combinations ofcomponents are contemplated to include homogeneous and/or heterogeneousmixtures, as would be understood by a person of ordinary skill in theart in view of the foregoing disclosure.

REFERENCES

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What is claimed is:
 1. A method for forming 2,5-furan dicarboxylic acid(FDCA), the method comprising: providing a reaction medium comprising a6-carbon aldaric acid, an acid catalyst, and an ionic liquid; anddehydrating and cyclizing the aldaric acid in the reaction medium toform 2,5-furan dicarboxylic acid (FDCA) as a reaction product.
 2. Themethod of claim 1, wherein the aldaric acid is selected from the groupconsisting of galactaric acid.
 3. The method of claim 2, furthercomprising: oxidizing galacturonic acid to form galactaric acid; andadding the galactaric acid to the reaction medium.
 4. The method ofclaim 2, further comprising: extracting pectin from a biomass material;hydrolyzing the pectin to form galacturonic acid; oxidizing thegalacturonic acid to form galactaric acid; and adding the galactaricacid to the reaction medium.
 5. The method of claim 4, wherein thebiomass material is selected from the group consisting of sugarbeetpulp, apple pomace, citrus pulp, and combinations thereof.
 6. The methodof claim 1, wherein the aldaric acid is selected from the groupconsisting of gularic acid, mannaric acid, and combinations thereof. 7.The method of claim 6, further comprising: oxidizing at least one ofguluronic acid and mannuronic acid to form at least one of gularic acidand mannaric acid, respectively; and adding the at least one of gularicacid and mannaric acid to the reaction medium.
 8. The method of claim 6,further comprising: extracting alginate from a biomass material;hydrolyzing the alginate to form at least one of guluronic acid andmannuronic acid; oxidizing the at least one of guluronic acid andmannuronic acid to form at least one of gularic acid and mannaric acid,respectively; and adding the at least one of gularic acid and mannaricacid to the reaction medium.
 9. The method of claim 8, wherein thebiomass material comprises macro algae.
 10. The method of claim 1,wherein the aldaric acid is selected from the group consisting ofglucaric acid.
 11. The method of claim 1, wherein the ionic liquidcomprises a cationic moiety selected from the group consisting of apyridinium, pyridazinium, pyrimidinium, pyrazinium, oxazinium,thiazinium, imidazolium, pyrazolium, thiazolium, isothiazolium,oxazolium, isoxazolium, and triazolium cationic moieties.
 12. The methodof claim 11, wherein the ionic liquid further comprises one or moreorganic substituents selected from the group consisting of alkyl groupsand aryl groups.
 13. The method of claim 11, wherein the ionic liquidfurther comprises a counter anion selected from the group consisting ofsulfate, hydrogen sulfate, nitrate, fluoride, chloride, bromide, iodide,methyl sulfonate, and fluoroborate anions.
 14. The method of claim 13,wherein the acid catalyst comprises an acid corresponding to the counteranion of the ionic liquid.
 15. The method of claim 1, wherein the acidcatalyst is selected from the group consisting of sulfuric acid, nitricacid, hydrofluoric acid, hydrochloric acid, hydrobromic acid, hydroiodicacid, methyl sulfonic acid, and fluoroboric acid.
 16. The method ofclaim 1, wherein the acid catalyst is selected from the group consistingof a liquid phase organic sulfonic acid.
 17. A method for forming2,5-furan dicarboxylic acid (FDCA), the method comprising: providing areaction medium comprising a 6-carbon aldaric acid and an acid catalyst;and dehydrating and cyclizing the aldaric acid in the reaction medium toform 2,5-furan dicarboxylic acid (FDCA) as a reaction product; whereinthe reaction medium substantially free from water, the reaction mediumcontaining less than 1 wt. % water before dehydrating and cyclizing thealdaric acid in the reaction medium to form the FDCA reaction product.18. The method of claim 1, wherein the reaction medium is substantiallyfree from alcohols, the reaction medium containing less than 1 wt. %alcohols before dehydrating and cyclizing the aldaric acid in thereaction medium to form the FDCA reaction product.
 19. The method ofclaim 1, further comprising: separating the FDCA reaction product fromthe reaction medium.
 20. The method of claim 1, comprising reacting anddehydrating the aldaric acid in the reaction medium at a temperatureranging from 50° C. to 200° C.
 21. The method of claim 1, comprisingreacting and dehydrating the aldaric acid in the reaction medium at apressure equal to or less than atmospheric pressure.